Date Calculator — Add, Subtract, Difference, Age and Business Days
This date calculator handles four common date math tasks in one place. Use the Add / Subtract tab to shift any starting date by days, weeks, months, years or business days, in either direction. Use the Difference tab to find the exact span between two dates, with the result broken down into total days, weeks, and a years / months / days breakdown. The Age tab returns an exact age as years, months and days, plus total days lived and a countdown to the next birthday. The Business Days tab adds or subtracts working days only, with an optional toggle to skip US federal holidays.
For example, 90 days from January 15 lands on April 15, a Wednesday. Adding 1 month to January 31 returns February 28 (or February 29 in a leap year), matching how spreadsheet date functions handle end-of-month overflow. The mini calendar highlights the start date, the result, and the dates in between.
Date Calculator
Add or subtract time, find the difference between dates, calculate exact age and business days
Resulting date
Start Result Between
Total difference
Start End Between
Exact age
Business days exclude Saturdays and Sundays. Optionally skip US federal holidays for the relevant year.
Resulting business day
Common date offsets from today
Offset
Date
Day of week
Frequently asked questions
When the destination month has fewer days, the calculator clamps to the last day of that month. So January 31 + 1 month = February 28 (or February 29 in a leap year). It will not roll over into March. This matches the behaviour of most spreadsheet date functions like EDATE.
Business days exclude Saturdays and Sundays. When you enable "Skip US federal holidays", the calculator also skips New Year's Day, Martin Luther King Jr. Day, Presidents' Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving and Christmas (using the official observed dates that fall in the year of the result).
By default the calculator returns the number of full days between two dates, which is what most projects, contracts and trip planners expect. Toggle "Include the end day" if you also want to count the end date itself — for example, a trip from June 1 to June 5 is 4 days of travel but 5 calendar days inclusive.
Age is computed by walking calendar months and days, not by dividing total days by 365.25. Someone born on February 29 will see their age tick over on February 28 in non-leap years and February 29 in leap years, matching how most countries compute legal age.
In the Add / Subtract tab the result is the exact calendar date, which can fall on any day of the week. If you specifically need to land on a weekday, switch to the Business Days tab — it skips Saturdays and Sundays automatically.
No. All dates are treated as plain calendar dates with no time-of-day or time-zone component. This is the right model for due dates, birthdays, anniversaries and contract terms, and it avoids the off-by-one errors that creep in when daylight saving time changes the length of a day.
All calculations use plain calendar arithmetic. Time zones and time-of-day are not considered.